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On my FM, the fuel pump starves for fuel if more than 5 gallons of fuel are out of the fuel cell. If it's topped off, it's good to go, but after drawing down 5 gallons- problems. Replaced the Facet pump, and the suction tube in the cell (both looked good) with no change.
Any thoughts?
plugged vent.
did you check this when checking the suction tube. Moses also told me that the braided fuel line to carb can some times develop pinholes you can not see. The result would be a lean run and possible detonation. It would show up in the top gear at full throttle.
Found the problem when checking the vent. Gently blew on the vent hose to make sure it was free. When I did, the hose at the 90 degree fitting at the top of the cell started to leak. The AN hose looked good- no marks or abrasions, but it was clearly leaking! So when the cell was full, the pump would work fine, but as the fuel level dropped, it became "easier" to suck air instead of fuel. Path of least resistance i guess. Ran the car yesterday without incident. Thanks for the vent check tip!Quote:
Originally Posted by sflaten
My cheapskate mentality bit me hard at COTA one year, I replaced the external lines, fuel pump, and breather/vent.....It would suck just enough air to let the carb go dry at the end of the straights.
Don't be like me, replace all fuel lines if they are more than like 4 yrs old or unknown. EVEN THE IN-TANK LINES! Believe me i know how much of a pain in the butt it is to pull the tank, but any amount of effort is worth it to not have power all the way down the straights like I had.
Yeah, as a "newbie", I was thinking the braided AN lines were a "forever" thing, as long as they didn't get physically compromised. More items on the to do list............Quote:
Originally Posted by mstephenson51
I had exactly the same problem... mid way through the race car essentially runs out of fuel. Changed everything in fuel system, and changed float height etc. Bought a second new Facet fuel pump and presto, works like a champ. Bill Weaver experienced the same problem and went through 3 new fuel pumps before he got one that worked well enough to pump against the additional head as fuel drained down. Try trading a known good fuel pump and see if that fixes the problem... then buy three fuel pumps hoping one of them actually works!
Todd,Quote:
Originally Posted by toddmcallister
It turns out the ongoing issue I was having with the Facet pumps wasn't actually the pump. The 3 pumps you mention were all brand new "Solid State" Facets, which all clattered but wouldn't pump fuel. I borrowed a spare from Brad, which had to be 15 years old if it was a day, and it worked perfectly. When I bench tested the 3 new ones, they all pumped perfectly, but wouldn't work on the car. After scratching my head until it was raw, I finally figured out that the only thing different between them working on the bench test and not working when mounted on the car was the switch. Made a jumper to bypass the switch, and what do you know...they all now work perfectly. Apparently the contacts on the fuel pump switch were glazed enough to not send enough current to run the "Solid State" pumps, but enough to run the old style "points" pump. I now have a lifetime supply of Solid State Facet pumps...LOL!! Anybody need one??
Just wanted to clarify a couple of points and expand on this thread.
The fuel line that can be the sneaky culprit is the line that goes from the fuel cell, to the pump. Over time this line can develop small pin holes. Because this line is under vacuum, you will not see or smell fuel leaking from it. while the car is running. When the cell is full, there is a siphoning effect, so the pump is not pulling very hard. Once the fuel level drops, the pump pulls harder, and depending on the condition of the fuel hose, will start to introduce air into the fuel stream. At some point you will not be able to feed the Carburetor bowl enough and you will start to starve the engine. This is actually a bigger problem than you think. Remember many of us are premixing fuel now, which carries oil to the engine to lube it. If there is no fuel in there, there is no oil, and this starving happens at full throttle at higher RPMs, which is when the engine needs the most lubrication.
That being said and starving is bad, like running the car out of fuel because you forgot to fill it up after the last session, or was going for a "qualifying" lap. Trust me, saving 6.6 lbs by running one gallon less than you need to finish the session is just not worth it in my opinion.
Back to the siphoning effect. If you run the Fuel Cell "Full" you will be putting less strain on the fuel pump, which will make it last longer. I always run the cars I maintain Full. Except maybe at the RunOffs for Qualifying, but still run enough fuel that it will not run out during that session.
When it comes to Fuel lines, fuel pump and oil lines. We replace all the fuel lines, and oil lines every Five years at a minimum. With the exception of the fuel line that goes from the cell to the pump, which we change every 3 years. The Ignition Switch, and Fuel pump switch we replace every 3 years as well. These are minimums, of course upon inspection of these items you may need to replace more often. If the anodizing on the fittings start to fade significantly, it might be time to change them.
As our cars get older, I see more and more parts that should have aged out YEARS ago, still hanging on. I have also seen a few of these parts fail on other competitors cars (FM and Non FM) spraying fuel and oil on HOT parts. Luckily I have not seen these fluids ignite, But that is not a reason to avoid preventative maintenance.
The fuel cells in the cars I maintain, also get replace every 5-6 years. Most cells will last at least 7 years. Most sanctioning bodies make you or suggest you replace your cell after 5. The manufacturer of the cell, will only "warranty" the cells for 5 years. Again I know this is a pricey item, but if you amortize the cost over 5-6 years, its really not that bad. I can not tell you how often a customer calls and says that they opened up their trailer and it wreaked of fuel. A lot of these trailers have wood floors, that are now soaked in fuel... In my opinion, it is better to be ahead of these aged out failures.
Not trying to scare anyone, just sharing my experiences. I get to hear and see a lot of stories.
Last thought, when diagnosing a fuel pick up problem. As soon as you experience a fuel pick up problem, come into the pits, if you have someone helping you that weekend, have them switch pick up lines, and go back out. Every once in a while the pick up line inside the fuel cell will develop a hole or crack, if you switch pick ups, and it "fixes" the starvation, then your problem is most likely inside the cell. If it didn't fix the problem, you may have a problem with both pick ups (which is unlikely) a problem with the cell to pump line. When we replace the fuel cell, we also replace the two pick up lines, the fuel cell flapper, and the fuel cap o ring.
Another point of inspection is the fuel regulator. This can also let air in the fuel system, but it will usually give you plenty of warning as it will leak a small bit of fuel before creating a larger air induction. In my experience Regulators RARELY fail from regulating pressure, but will start to leak over time (Very long time).
I know I can be long winded...but I hope this helps.
Moses
<br>Now that Moses solved the fuel starving issue, next on the list is fuel pressure to the carb. Fiddled with the regulator trying to solve the starving issue, and not sure where the pressure regulator should be set. What PSI value to the carb is correct?<br>How sensitive is the carb to PSI variations?Thanks! Quote:
Originally Posted by MosesSmithRacing
I had the exact same thing happen to me. I plugged one end, put some air pressure in the other and put the hose in water. Looked like a fish tank air stone. The braided hose looked just fine.Quote:
Originally Posted by sflaten
Can you switch to PTFE lines to last “forever”?